Subscription add in Redhat linux

• SSH / Get console of the shell of the desired Red Hat system you want to subscribe with the subscription
• run subscription-manager register command andsubscription-manager attach --pool=<POOL_ID>, the pool id can be found using subscription-manager list --available, this pool-ID is the unique ID respective to your subscription
• Internet connectivity to the system is required as the system will get authentication of the subscription from access.redhat.com
• verify the subscription is current/invalid from subscription-manager status command, If the output says  " Current " means the system is registered with proper subscription, anything other than this will come as an output saying "Invalid "
• The subscription can be attached to any Red Hat system, where the environment is started from RHEL 5.7 to the latest (7.5) one
• If the system had any previously attached subscription, please run these two commands one-by-one subscription-manager clean ; subscription-manager refresh at the system to clear out the previous metadata
• If the system had any previously added repository manually (not through Red Hat subscription) please run these command rm -fr /etc/yum.repos.d/* to delete any Repository configuration file which're not attached through a valid Red Hat subscription.
• You can also see the system attached to the subscription from your purchase account at access.redhat.com where the subscription will be shown attached to which system, the Hostname/ UUID.  
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  Resolution

  If you continue to see applicable errata displayed in RHSM, it can mean one of a couple of things that need to be addressed:
  
• The system has not checked in recently, and there is a discrepancy between what you see in the Customer Portal and what is actually installed on your system. In this case, you may want to check which errata are available on your system and force a check in and run yum update again:

# yum update
# rm -f /var/lib/rhsm/packages/packages.json
# service rhsmcertd stop 
# rhsmcertd --now

Note: After forcing your system to check in again, please wait up to four hours for the errata data on RHSM to update to their correct data.